1. Technical Field of the Invention
The present invention relates to mixing of frequency-modulated signals to deliver an output signal at a frequency obtained by combining the frequencies of the first and second signals.
2. Description of Related Art
Known mixing devices use two variable resistance stages, connected in series between a power supply voltage and a reference voltage, the resistance variation of each stage being controlled by one of the two signals to be mixed.
Conventionally, each of these two stages is implemented in the form of two cascoded transistors, the variations of the input signals causing variations of the current flowing in the transistors. All the transistors conduct one of the signals to be mixed, such that they must each satisfy strict operating requirements.
In particular, in order to reduce the area of circuit used and the consumption of electrical energy, these transistors present a high internal resistance and need to operate at high frequencies with low voltages. Consequently, these transistors present a high voltage swing at their terminals, which reduces the useful power available on the output signal.
However, in numerous applications, such as telecommunications, it is essential to have a predetermined output power.
Consequently, there is a problem concerning power available at the output of the existing mixing devices.
There is accordingly a need to resolve this problem by means of a mixing device suitable for delivering a higher output power level.